The embodiment relates to a light emitting device, a light emitting device package, and a lighting system.
A light emitting device (LED) includes a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode can be formed by combining group III-V elements of the periodic table. The LED can represent various colors by adjusting the compositional ratio of compound semiconductors.
When forward voltage is applied to the LED, electrons of an n layer are combined with holes of a p layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be generated. This energy is realized as heat or light, and the LED emits the energy in the form of light.
A nitride semiconductor represents superior thermal stability and wide band gap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been developed and extensively used.
Nitride semiconductor light emitting devices may be classified into lateral type light emitting devices and vertical type light emitting devices according to the positions of electrode layers.
In the lateral type light emitting device, a nitride semiconductor layer is formed on a sapphire substrate, and two electrode layers are disposed on the nitride semiconductor layer.
The light emitting device emits light through the recombination of electrons produced in an n type structure and holes produced in a p type structure.
Meanwhile, since an electron has a mass and mobility greater than those of a hole, the overflow of electrons is prevented by using an electron blocking layer including a material, such as p type AlGaN, representing a high potential barrier.
Meanwhile, in order to allow the LED to emit light, the concentration of holes is important more than that of electrons. However, the incorporation of magnesium (Mg) is competitively performed under the environment having a higher Al content of an electron blocking region, so that the level of Mg becomes lowered in the initial stage of growing a p type electron blocking layer, which is called an Al memory-effect. The Al memory-effect serves as one of primary causes of interrupting hole injection into the electron blocking layer, thereby degrading light efficiency.